Titanium tungsten alloys produced by additions of tungsten nanopowder

ABSTRACT

Disclosed herein are titanium-tungsten alloys and composites wherein the tungsten comprises 0.5% to 40% by weight of the alloy. Also disclosed is a method of making such alloys and composites using powders of tungsten less then 3 μm in size, such as 1 μm or less. Also disclosed is a method of making the titanium alloy by powder metallurgy, and products made from such alloys or billets that may be cast, forged, or extruded. These methods of production can be used to make titanium alloys comprising other slow-diffusing beta stabilizers, such as but not limited to V, Nb, Mo, and Ta.

This application claims the benefit of domestic priority to U.S. Provisional Patent Application Ser. No. 60/563,009, filed Apr. 19, 2004, which is herein incorporated by reference in its entirety.

Disclosed herein are titanium-tungsten alloys and composites. Also disclosed is a method of making such alloys and composites using nanopowders of tungsten and optionally comprising slow-diffusing beta stabilizers, such as but not limited to V, Nb, Mo, and Ta.

While Ti alloys strengthened by W are generally desirable because they are strong wear resistant alloys, such alloys are difficult, if not impossible, to prepare by typical techniques. For example, in a casting process, W generally completely dissolves in the molten Ti during the melting step. As the resulting ingot solidifies beta-rich large, elongated islands form between the dendrites of the solidified casting. These resulting defects lead to poor mechanical properties in the final product.

Until the present disclosure, the preparation of Ti—W by powder metallurgy (P/M), was not commercially viable because of the high melting point and slow diffusivity associated with W that causes it to remain segregated as discrete or undissolved particles. Ti—W alloys are mentioned in the literature for use as sputtering targets and in thin film applications; however, these alloys are tungsten (W) based with typically 10% or less Ti.

Literature that does describe Ti based alloys comprising W describes W being added to form a particulate dispersion. For example, M. Frary, S. M. Abkowitz, and D. C. Dunand, “Microstructure and Mechanical Properties of Ti/W and Ti-6Al-4V/W Composites Fabricated by Powder-Metallurgy,” Materials Science and Engineering A344 (2003) 103-112, which is herein incorporated by reference, shows that partially diffused W dispersions in Ti powder (Commercially Pure “CP” Ti) and Ti-based alloys (Ti-6Al-4V) increases strength with an acceptable loss in ductility. The alloys described in Frary et al. comprise 3 μm to 10 μm tungsten powders that are too large to completely diffuse.

SUMMARY OF THE INVENTION

The present disclosure avoids the aforementioned problems by using tungsten nanopowder. As used herein, nanopowder is defined as powders less than 1 micron, such as powders ranging from about 8 angstroms (the detection limit of electron microscopy) to less than 1 micron. The Inventors have discovered that the use of W nanopowder in the preparation of Ti—W alloys allows the W to completely diffuse into the Ti matrix during a typical P/M sintering cycle.

In one embodiment, completely diffused W nanopowder forms an alpha/beta or all beta microstructure, or as alpha/beta or all beta microstructure containing a dispersion described as “beta phase islands.” Beta phase islands are a microscopic beta rich structure dispersed throughout an alpha, alpha/beta or all-beta microstructure. These dispersions result in Ti/W alloys with properties that are superior to a dispersion of partially diffused W particulates produced using Ti powder 3 μm or larger. In fact, the commercially pure (CP) Ti with 10% W containing dispersions of beta phase islands can have properties superior to Ti-6Al4V. In addition, the Ti-6Al-4V with 10% W can have annealed properties equivalent to the highly alloyed all-beta alloys that require solution treatment and aging to fully develop their properties (e.g. Ti-13V-11 Cr-3Al).

In accordance with the present disclosure, W nanopowder can be blended with CP (commercially pure) Ti powder and, in the case of an alloy, blended with Ti powder, other elemental powders or with master alloy powders, which is defined as the mixture of starting metal powders used to form the resulting alloy by powder metallurgy processing. The powder blend is compacted, sintered and may or may not be hot isostatic pressed. The product may be subjected to additional processing, such as, forging, casting, or extrusion.

A casting billet may also be prepared in the manner described above and then cast to shape. Ti—W master alloy additions can also be prepared by the methods disclosed in this invention. These master alloy additions can be used in casting of Ti—W or may be made into master alloy powder by attrition for use in P/M processing.

The total diffusion of W, as disclosed herein, results in an alpha/beta phase microstructure in CP titanium typical of commercial alpha/beta alloys. In alpha/beta alloys the total diffusion of W results in a near beta or all beta microstructure. The Ti—W alloys also have properties that are superior to conventional Ti-6Al-4V. Further the Ti—W alpha/beta and all-beta alloys can be solution treated and aged in much the same way as conventional heat treatable Ti alloys.

Disclosed herein is a method of making an alloy having a uniform dispersion of beta phase islands within a Ti matrix. According to this aspect, this uniform dispersion of beta phase islands can be controlled within the Ti matrix by adjusting the P/M sintering time and/or by manipulating the W powder size to a range from 8 angstroms to less then 3 μm, such as less than 1 μm. The beta phase island dispersion results in improved room and elevated temperature properties.

In another aspect of the disclosure, the above-described method based on tungsten (W) can be used with other beta stabilizers, such as but not limited to V, Nb, Mo, and Ta. In this embodiment, the powder size of the particular beta stabilizer is related to the beta stabilizer's diffusivity at the sintering temperature of Ti.

The creation of a uniform dispersion of beta phase is dependent on, among other things, the size of the beta stabilizer powder. In one embodiment, the beta stabilizer powder is less then 3 μm, such as less than 1 μm. The powder size used according to the present disclosure is also related to the beta stabilizer's diffusivity at the sintering temperature. In addition, the powder size range can depend on the desired matrix microstructure (i.e. alpha/beta or all beta), the size and number of beta phase islands and the desired amount of partially diffused beta stabilizer (residual undiffused particulate) with the beta phase islands, such as at the center of the beta phase islands.

Partially dissolved particles of the beta-stabilizing addition, such as partially dissolved particles of W, V, Nb, Mo, or Ta, may be present within, such as at the center of, the beta phase islands and may contribute to the strengthening mechanism.

The properties of Ti metal matrix composites containing particulate reinforcement of titanium carbide (TiC), titanium boride (TiB) or titanium diboride (TiB₂) can also be enhanced by W nanopowder additions or the addition of sub-sieve sized powder of other beta stabilizers.

The accompanying micrograph that is incorporated in and constitutes a part of this specification, illustrates one embodiment of the invention and together with the description, serve to explain the principles of the disclosure.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a scanning electron micrograph of a titanium-tungsten alloy according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present disclosure is directed to a composition of a titanium based alloy comprising a titanium material and tungsten in an amount ranging from 0.5% to 40% by weight. In one embodiment, the W powder addition used to make the alloy has an average diameter of less then 3 μm in size, such as less than 1 μm, and ranging from 8 angstroms to less then 1 μm as measured by the Fisher sub-screen size method, electron microscopy and/or photon correlation spectroscopy.

The titanium in the Ti/W alloy described herein may comprise CP Ti powder or a Ti alloy, such as Ti-6Al-4V.

The composition may comprise an alternative or additional slow diffusing beta stabilizer chosen from but not limited to V, Nb, Mo, and Ta. Such stabilizers will lead to an alloy containing dispersions of beta phase islands or an all beta structure with dispersions of partially dissolved beta stabilizer. In one embodiment, the beta phase islands contain undiffused particulate beta stabilizer at the core of the islands.

As described in the prior art, “beta flecks”, are generally a form of beta phase islands that are well-known as a defect. See, for example, “Powder Metallurgy of Titanium Alloys,” by Froes and Smugeresky, The Metallurgical Society of AIME, Warrendale, Pa. 1980; ASM Online Handbook, “Wrought Titanium and Titanium Alloys—Wrought Titanium Processing,”; “Processing of Titanium and Titanium Alloys—Secondary Fabrication,” Y. G. Zhou, J. L. Tang, H. Q. Yu, and W. D. Zeng, “Effects of Beta Fleck on the Properties of Ti-10V-2Fe-3Al Alloy,” Titanium 1992 Science and Technology, The Minerals, Metals and Materials Society, Warrendale, Pa. 1992, Vol 1, pp 513-521; and http://mse-p012.eng.ohio-state.edu/fraser/mse663/AlphaBeta JCW.pdf, “Properties and Applications of α+β Ti Alloys, which are all incorporated herein by reference.

The occurrence of beta fleck defects is generally unpredictable, and usually results in poor properties, and thus may lead to the premature failure of a component. Contrary to the teachings of the prior art, the present disclosure provides for the creation of uniform dispersions of beta phase islands that can improve the mechanical properties of Ti and its alloys. The beta fleck defect occurs in alpha-beta and near beta alloys where segregation of alloying elements results in localized regions depleted in alpha stabilizers (e.g. aluminum) or with an excess of beta stabilizers (e.g. molybdenum). These regions then transform to the beta phase resulting in beta flecks. Contamination of powder or castings by tramp particles of a beta stabilizer, such as W, can also result in beta flecks.

The present disclosure teaches that controlled dispersions of the so-called “beta fleck”, herein termed “beta phase islands”, can be beneficial and improve the properties of titanium and its alloys.

In another embodiment, the alloy has a microstructure that comprises all-alpha phase, alpha/beta phases and all beta phase, or all-alpha phase and alpha/beta phases comprising a dispersion of beta phase islands. The beta phase islands optionally include partially diffused beta stabilizer within the beta phase islands, such as at the center of the beta phase islands.

Also described herein is a powder metallurgical method of making the above-described composition. This method comprises:

-   -   blending a titanium material powder with a tungsten powder to         form a blended powder that comprises from 0.5% to 40% by weight         of tungsten powder having an average diameter less then 3 μm in         size, such as ranging from 8 angstroms to less than 1 μm, such         as ranging from 10 nm to 500 nm;     -   compacting the blended powder; and     -   sintering the compacted and blended powder, wherein     -   the sintered compact can then be hot isostatically pressed if         necessary.

After powder metallurgical processing as described above the part may be further processed by techniques including, but not limited to casting, forging, and extrusion.

In one embodiment, the alloy described herein may be used in implantable medical devices, such as orthopedic implants, including spinal implants, disc prostheses, nucleus prostheses, bone fixation devices, bone plates, spinal rods, rod connectors, knees, and hip prostheses, dental implants, implantable tubes, wires, and electrical leads. In other embodiments, the alloy may be used in drug delivery devices, including stents.

The alloy disclosed herein may also be formed into a product, such as a billet for further processing. In other embodiment, the product may be an automotive component such as valves, conrods, and piston pins.

The product may also comprise an armored vehicle component such as tank track center guides and undercarriage parts.

In another embodiment, the product may comprise a tool or die material for metal casting.

The product may also be an aircraft component such as a turbine rotor, and a leading edge of a helicopter rotor blade.

All amounts, percentages, and ranges expressed herein are approximate.

The present invention is further illuminated by the following non-limiting example, which is intended to be purely exemplary of the invention.

EXAMPLE

A powder metallurgy technique was used to produce a tungsten containing titanium alloy. Using this method, beta phase island dispersions were created in CP Ti and in Ti-6Al-4V with 10% by weight W. In this example, nanopowder 30 to 45 nanometers (0.003 to 0.004 μm) in size with a specific surface area of between 7 to 10 m²/g was blended with CP Ti powder and processed as described above. These W nanopowders were also blended with CP Ti and master alloy powders to form the Ti-6Al-4V composition shown in Table 1.

The W nanopowder was taken into solution in the Ti matrix on sintering the compacted blend, forming an alpha/beta structure with a uniform beta phase island dispersion.

FIG. 1 shows that the W nanopowder completely diffused to form a beta phase island dispersion in the alpha/beta matrix. The diffusion of the W nanopowder transformed the all alpha microstructure typical of CP Ti to alpha/beta containing a dispersion of beta phase islands. In this case there was no evidence of any undissolved W.

Table 1 shows that 10% W nano-sized powder addition substantially improved the strength of CP Ti resulting in twice the strength of CP Ti, as well as a higher strength then Ti-6Al-4V with roughly equivalent ductility. In the Ti-6Al-4V containing composition, the W nanopowder addition resulted in a 30% improvement in strength while maintaining satisfactory ductility. TABLE 1 The Effect of 10% W Nano-sized Powder Addition on the Mechanical Properties of CP Ti and Ti-6Al-4V Ultimate Tensile Yield Reduction Material Strength Strength in Area Composition (psi) (psi) Elongation (%) (%) Ti 75,110 59,595 24 46 Ti + 10% W 147,320 131,515 15 37 Ti-6Al-4V 137,605 124,700 14 28 Ti-6Al-4V + 10% W 178,350 171,100 9 20

Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 

1. A composition comprising a titanium alloy, said alloy comprising tungsten in an amount ranging from 0.5% to 40% by weight of said alloy, wherein the tungsten has an average diameter less then 3 μm in size.
 2. The composition of claim 1, wherein the tungsten powder has an average diameter ranging from 8 angstroms to 1 μm or less.
 3. The composition of claim 2, wherein the tungsten powder has an average diameter ranging from 10 nm to 500 nm.
 4. The composition of claim 1, comprising at least one beta stabilizer chosen from V, Nb, Mo, and Ta.
 5. The composition of claim 1, wherein said alloy comprises dispersions of beta phase islands.
 6. The composition of claim 5, wherein said beta phase islands comprise undiffused particulate beta stabilizer at the core of said islands.
 7. The composition of claim 1, wherein said titanium material comprises a material chosen from Ti powder and Ti alloy.
 8. The composition of claim 1, wherein said alloy has a microstructure that comprises alpha/beta phases, all beta phases, or alpha/beta phases comprising a dispersion of beta phase islands.
 9. The composition of claim 8, wherein said beta phase islands include partially diffused beta stabilizer within the beta phase islands.
 10. The composition of claim 1, further comprising at least one particulate material chosen from titanium carbide (TiC), titanium boride (TiB), titanium diboride (TiB₂) or combinations thereof.
 11. A powder metallurgy method of producing a tungsten comprising titanium alloy, said method comprising: blending a titanium containing powder with a tungsten containing powder to form a blended powder, said blended powder comprising tungsten powder in an amount ranging from 0.5% to 40% by weight of said alloy, wherein said tungsten powder has an average diameter less then 3 μm in size; compacting the blended powder; sintering the compacted and blended powder to form a tungsten containing titanium alloy; and optionally subjecting the sintered tungsten containing titanium alloy to hot isostatic pressing.
 12. The method of claim 11, further comprising subjecting the sintered tungsten containing titanium alloy to a process chosen from casting, forging, and extrusion.
 13. The method of claim 11, wherein the tungsten containing powder has an average diameter ranging from 8 angstroms to 1 μm or less.
 14. The method of claim 13, wherein the tungsten containing powder has an average diameter ranging from 10 to 500 nm.
 15. The method of claim 11, wherein the blended powder further comprises at least one beta stabilizer chosen from V, Nb, Mo, and Ta.
 16. The method of claim 11, wherein the blended powder further comprises at least one particulate material chosen from titanium carbide (TiC), titanium boride (TiB), titanium diboride (TiB₂) or combinations thereof.
 17. The method of claim 11, wherein said tungsten containing titanium alloy contains dispersions of beta phase islands.
 18. The method of claim 17, wherein said beta phase islands contain residual beta stabilizer at the core.
 19. The method of claim 11, wherein said titanium containing powder comprises a Ti powder or a Ti alloy.
 20. The method of claim 19, wherein said Ti alloy comprises Ti-6Al-4V.
 21. The method of claim 11, wherein the tungsten containing titanium alloy has a microstructure that comprises all-alpha phase, alpha/beta phases, or all-beta phase, or all-alpha phase or alpha/beta phases comprising a dispersion of beta phase islands.
 22. The method of claim 21, wherein said beta phase islands include partially diffused beta stabilizer within the beta phase islands.
 23. A product comprising the composition of claim
 1. 24. The product of claim 23, wherein said product is an orthopedic device chosen from knee, hip, spinal, and dental implants.
 25. The product of claim 23, wherein said product is an automotive component chosen from valves, connecting rods, piston pins and spring retainers.
 26. The product of claim 23, wherein said product is an military vehicle component chosen from tank track, suspension, and undercarriage parts.
 27. The product of claim 23, wherein said product is a tool or die material for metal forming chosen from shot sleeves, plungers and dies.
 28. The product of claim 23, wherein said product is an aircraft component chosen from a turbine rotor, and a leading edge of a helicopter rotor blade, tubing, valves and fittings.
 29. The product of claim 23, wherein said product is a billet for subsequent casting, forging or extrusion.
 30. A powder metallurgy method of producing a titanium containing product, said method comprising: blending a titanium containing powder with a tungsten containing powder to form a blended powder, said blended powder comprising tungsten powder in an amount ranging from 0.5% to 40% by weight of said alloy, wherein said tungsten powder has an average diameter less then 3 μm in size; compacting the blended powder; and sintering the compacted and blended powder, said method optionally comprising a post-sintering process chosen from hot isostatically pressing, casting, forging and extrusion.
 31. The method of claim 30, wherein said product is an orthopedic or dental implant.
 32. The method of claim 30, wherein said product is a billet that is subjected to at least one post-sintering process chosen from casting, forging, and extrusion. 